One of the biggest problems caused by vehicles using fossil fuel such as gasoline and diesel is the creation of air pollution. Technology of using a secondary battery, which can be charged and discharged, as a power source for vehicles has attracted considerable attention as one method of solving such a problem. As a result, electric vehicles (EV), which are operated using only a battery, and hybrid electric vehicles (HEV), which jointly use a battery and a conventional engine, have been developed and some are commercially available. A nickel-metal hydride (Ni-MH) secondary battery has mainly been used as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV). A lithium-ion battery has also been used recently.
High power and large capacity are needed for such a secondary battery to be used as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV). To this end, small-scale secondary batteries (unit cells) are connected in series to form a battery module and a battery pack. Where appropriate, small-scale secondary batteries (unit cells) are connected in series and in parallel to form a battery module and a battery pack.
Generally, such a battery pack has a structure to protect battery modules, each of which includes secondary batteries mounted therein. The structure of the battery module may be varied based on the kind of vehicles or the installation position of the battery pack in vehicles.
In one structure to effectively fix large-capacity battery modules, a battery pack is constructed such that battery modules are fixed to a rigid lower plate. In this structure, each individual battery module is fixed to the lower plate such that reliability of the battery pack such as durability and vibration resistance is secured through structural rigidity of the lower plate. However, this structure has a problem in that there is a need to secure sufficient rigidity of the lower plate.
FIG. 1 is an exemplary perspective view of a conventional battery pack including a single battery module as an example of a battery pack having the above structure.
Referring to FIG. 1, a battery pack 100 includes unit modules 10, each of which has secondary batteries mounted therein, a lower plate 20, a pair of side support members 30, and a pair of top support members 40.
The unit modules 10 are stacked at the top of the lower plate 20 in a state in which the unit modules 10 are vertically erected. The side support members 30 are disposed in close contact with the outer sides of the outermost unit modules 10 in a state in which the lower end of each of the side support members 30 is fixed to the lower plate 20.
The top support members 40 are connected between the upper parts of the side support members 30 to interconnect and support the side support members 30.
However, the battery pack with the above construction has a small capacity since the battery pack includes only a single battery module. Thus, it is difficult to apply the battery pack with the above construction to external devices such as vehicles that require high power and large capacity.
Therefore, there is a great need to provide a battery pack that includes battery modules arranged in two or more rows to achieve high power and large capacity and has a specific structure in which durability of the battery pack can be secured against vibration and impact and the battery pack can be compactly constructed.